That project has an interactive playground that essentially describes and demonstrates how it works: https://ffmpegwasm.netlify.app/playground
This also means that despite being a locally hosted ffmpeg frontend, it's still slower than native ffmpeg and bound to WASM limits like file size (still a generous 2GB for images and audio, but not as viable for big video conversions).
Still weird that this project doesn't seem to acknowledge that anywhere.
Libraries
A big thanks to FFmpeg (audio, video), libvips (images) and Pandoc (documents) for maintaining such excellent libraries for so many years. VERT relies on them to provide you with your conversions.
https://github.com/VERT-sh/VERT/commit/8f8ea34483cab76e27204...
We use QuickJS (the JavaScript runtime he authored) in Minecraft (Bedrock) where even more developers use it to mod Minecraft. It's a huge pyramid of developers!
Checking out Bellard's website is a great high level list of works: https://bellard.org/
The dude can wrap his head around literally anything. Him and Torvalds are truly exceptionally capable people.
The things he built are:
ffmpeg, which basically implements a bunch of specs for codecs
Qemu, which basically implement a bunch of specs for CPUs
TinyC / QuickJS, which basically implement a bunch of specs, mainly those for C and JS.
That LTE thing, which, surprise surprise, implements a bunch of specs.
He seems to be a God of turning specs into working code, not necessarily a GOd of programming in general.
This kind of mental flexibility is what I really admire.
Don't get me wrong, I find him to be an elite dev, but more for the incredible ability to hold a spec in his head in sufficient detail - and do that multiple times.
Reading that list of projects is quite humbling. I've always wanted to make stuff like that.
https://newbeelearn.com/tools/videoeditor/
and this one also outputs ffmpeg command as well.